The present invention relates to filters for fluids in conduits, comprising                a tubular filter housing,        a filter basket coaxially and rotatably arranged in the filter housing        and a stationary flushing pipe piece for removing substances that have been retained by the filter basket,        said piece subsequently covering parts of the filter basket, and        being connected to means for removing these substances.        
Filters of this type are well known from FR 2 609 644. They are primarily for cleaning the cooling water for heat exchangers, such as in power stations, and are there inserted in the cooling water supply.
The well known filter has a filter basket with a screen surface extending across the free cross section of the filter housing and functions according to the so-called backflushing principle. Radial separating webs on the screen surface form filter chambers as parts of the filter basket. The filter basket is attached on a concentric shaft rotatably supported by a hub held by radial spokes. The filter basket is driven by a motorized rotary drive arranged on the outside of the filter housing, the drive pinion of which runs in mesh with outer toothing of the filter basket. The flushing pipe piece is arranged in a stationary position on the upstream side directly at the open side of the filter chambers and connected to a suction conduit through the side wall of the filter housing. If a suction is created in the flushing pipe piece via this conduit and applied from there to the filter chamber which is currently covered by the flushing pipe piece, substances retained in the filter basket in this filter chamber, such as dirt or the like, are released from the filter chamber and removed to the outside by the flushing pipe piece through the suction conduit. The suction conduit is periodically operated or depending on the amount of dirt in the filter chambers. The filter basket is caused to rotate by the rotary drive so that one filter chamber after the other is exposed to the suction effect of the flushing pipe piece and thus cleaned.
A similar filter is known from FR 2 716 530, wherein a filter basket with a screen surface and with a subdivision in filter chambers is coaxially and rotatably arranged also in a filter housing. The filter is arranged at the cooling water outlet of heat exchangers. It is used to catch in the filter chambers cleaning bodies having circulated through the conduits of a heat exchanger, and removed from there by the application of the backflushing principle. Again, the rotary drive of the filter basket is by an outer toothing on the filter basket running in mesh with a pinion of a gearbox driven by an external electric motor. A pipe piece is arranged on each side, upstream and downstream, on this filter basket. The two pipe pieces cooperate. Cooling water is introduced into the downstream pipe piece under pressure, which passes through the screen surface of each filter chamber covered by the pipe piece for removing the cleaning bodies retained there and caused to exit via the upstream pipe piece and an exit conduit connected thereto.
A further filter of this type having a backflushing system is known from EP 0 897 096 B1, which is both for cleaning cooling water and for catching cleaning bodies from the cooling water flow. For this purpose, again, a filter basket with a screen surface is coaxially supported within a tubular filter housing and can be rotatably driven there. The rotary drive also consists of an outer toothing on a filter basket running in mesh with a drive pinion rotatably supported in a boss of the filter housing and driven by a motor arranged outside of the filter housing. In the exemplary embodiment of this document, the housing of this filter arranged on the cooling water outlet of a heat exchanger has a pressurized-water supply line on the downstream side of the filter basket and a flush-out conduit for flushing water on the upstream side above the filter basket. Also in this case, filter chambers are formed by radial separating webs on the upstream side on the screen surface of the filter basket. On the downstream side of the filter basket, connected to the pressurized water supply conduit, there is a pressurized pipe piece which is faced by a segment-shaped plate on the upstream side above the filter chambers, for forming a flow-free space in that filter chamber which is currently between the pressurized pipe piece and the plate. By opening the pressurized water supply, pressurized water flows through the section of the screen surface lying above the pressurized pipe piece and through the filter chamber arranged here, carries away the cleaning bodies caught in the filter chamber and exits together with them via the flush-out conduit.
Irrespective of whether the described backflushing principle is used in filters upstream of the cooling water inlet of heat exchangers for cleaning cooling water of dirt particles or the like, or for catching and removing cleaning bodies at the cooling water outlet of a heat exchanger, the force transmission for the rotary drive of the filter basket is always carried out by means of a toothed rim on the circumference of the filter basket within the filter housing. A pinion driven by an external motor is in mesh with the toothed rim. Depending on the structure, either the drive shaft of the motor passing through the filter housing or the gear box arranged within the filter housing have to be made fluid-proof. The manufacture and maintenance of this driving system for the filter basket are very bothersome.
A further drawback of this drive system is its lack of operation safety. Due to the axial and radial stresses acting on the screen surface and the filter basket due to the cooling water flow in combination with the rotary movement, the tolerances of the rotary bearing and the rotary drive of the filter basket are very difficult to control. Therefore, the rotary drive and rotary bearing of the filter basket are extremely prone to failure. Moreover, the motor of the well-known filters needs structural space and protection outside of the filter housing. The overhead for operational checks and for maintenance and repair of systems of this type is therefore high.
An alternative to this filter structure is shown in EP 0 268 752 B1, wherein a rotatably supported suction shoe as a flushing pipe piece rotates below a fixed filter basket with filter chambers on the upstream side. The motor for the rotary drive of the suction shoe can optionally be arranged within the filter housing or outside of it.